Stateless

iptables -A INPUT -i eth0 -d 192.168.0.0/24 -p tcp -m multiport --sports 20,21,22,25,80,110,443 -m tcp --tcp-flags ACK ACK -j ACCEPT

iptables -A OUTPUT -o eth0 -s 192.168.0.0/24 -p tcp -m multiport --dports 20,21,22,25,80,110,443 -m tcp --tcp-flags SYN SYN -j ACCEPT

iptables -A OUTPUT -o eth0 -s 192.168.0.0/24 -p tcp -m multiport --dports 20,21,22,25,80,110,443 -m tcp --tcp-flags ACK ACK -j ACCEPT